1. Field of the Invention
The present invention relates to a magnetic head used in a magnetic disk device, a magnetic tape device and so forth, and more particularly, to a magnetic tunnel junction magnetoresistive head (MR head) having a high sensitivity.
2. Description of the Prior Art
A magnetic information recording device such as a magnetic disk device, a magnetic tape device and so forth has been always required to record information at a higher density. Since a higher recording density causes reduction of a reproduced signal of a magnetic head, it is essential to develop more practical magnetic head in order to improve a recording density.
Predominant one of current high-density magnetic recording magnetic heads is a so-called composite magnetic head corresponding to a composition of a read magnetic head and a write magnetic head. In order to improve a reproducing sensitivity, there has been used as a read head an MR head based on a magnetoresistive effect or a giant magnetoresistive (GMR) head based on a GMR effect which has a higher sensitivity.
The change rates of the electric resistance caused by the magnetoresistive (MR) and giant magnetoresistive (GMR) field used in a prior art magnetic head are about 2-3% and about 5-10%, respectively. The larger the change rate of the electric resistance is the higher the reproduced output of the magnetic head is. Therefore, there has been demanded a magnetoresistive material having a higher change rate of the electric resistance. As one of materials potentially providing a higher change rate of the electric resistance, there is a material having a tunnel junction magnetoresistive effect (which will be referred to as a tunnel junction MR, hereinafter).
The tunnel junction MR is a phenomenon in which an electric resistance in a tunnel junction between two stacked ferromagnetic layers with an insulated layer disposed therebetween varies with the angle formed by the magnetization directions of the respective ferromagnetic layers. That is, the tunnel junction MR material has the maximum electric resistance when the magnetization directions of the both layers are oriented parallel to each other but in opposite directions, and has the minimum electric resistance when the magnetization directions are oriented parallel to each other. Accordingly, if one of the magnetization directions of the ferromagnetic layers is pinned or fixed while the other is rotated according to an external magnetic field, the electric resistance of the tunnel junction MR material is correspondingly changed. This effect is highly similar to that of a GMR spin valve film. However, the current must be passed parallel to the ferromagnetic layers in the spin valve film, whereas the current must be passed through the tunnel junction (in a direction perpendicular to the junction) in the tunnel MR material. In the spin valve film, even when the current is passed through the ferromagnetic layers in a direction perpendicular to the interface therebetween, the electric resistance becomes very small and the change in the electric resistance becomes small, because the intermediate layer is electrically conductive. On the other hand, in the tunnel junction MR material, the change in the electric resistance is much larger than that of the spin valve film, because the intermediate layer is a thin insulated layer. In order to put the tunnel junction MR material in practical use, the electric resistance of the tunnel junction MR material should be small enough to have the order of 10 to 102 ohms. Since the tunnel junction resistance is abruptly increased when the thickness of the insulated layer provided between the magnetic layers increases, it is demanded in the tunnel junction MR material that the insulated layer is very thin and has a high insulating property. In the original tunnel junction MR material, the stable formation of its element was very difficult, because it was difficult to form the insulated layer. However, recent studies have found that a good insulated layer of aluminum oxide can be formed, so that there can be formed a tunnel junction MR film, which has the change rate of about 20% at room temperature, with a good reproducibility.
In JP-A-10-162327, a magnetoresistive head which uses a magnetic tunnel junction and linearly responds to a magnetic field from a magnetic medium is disclosed.
Hereinafter, in connection with aforementioned explanation, a ferromagnetic layer, which has the fixed magnetization direction, of ferromagnetic layers forming the tunnel junction of the tunnel junction MR is called xe2x80x9ca magnetization pinned layerxe2x80x9d, and the other having the freely rotatable magnetization direction is called xe2x80x9ca magnetization free layerxe2x80x9d.
In a prior art MR (GMR) head of a most general structure, current is passed from one of electrodes formed in an identical plane to the other electrode through an MR (GMR) layer. On the other hand, in a tunnel junction MR head, unlike the prior art MR or GMR head, current must be passed through the tunnel junction in a direction perpendicular thereto. To this end, one electrode must be disposed below the tunnel junction made up of the magnetization pinned layer, an insulated layer and the magnetization free layer to pass a detection current between one electrode and the other electrode connected to an upper part of the tunnel junction. It is also required to provide layers for applying a bias magnetic field, which directs the magnetization of the magnetization free layer uniformly in a desirable direction and is for linearly responding to a magnetic field from a medium, at both ends of the magnetization free layer. In this connection, however, these layers must be isolated from the electrodes, the magnetization pinned layer and the magnetization free layer. In this way, the tunnel junction MR head of the structure wherein any of the electrodes, the magnetization pinned layer and the magnetization free layer are not in the same plane, is largely different in structure from the prior art MR (GMR) head. Therefore it is difficult to manufacture the tunnel junction MR head with use of a process of manufacturing the prior art MR head.
It is therefore a first object of the present invention to provide a tunnel junction MR head of a structure similar to that of the prior art head, which can be easily manufactured with use of the manufacturing process of the prior art head.
A magnetic head is manufactured by machiningly cutting magnetic heads formed on a substrate into individual separate heads and by polishing a surface of each head opposed to a medium. In an ordinary MR head structure, a part of an MR layer is exposed to an air bearing surface and is mechanically cut and polished simultaneously with the substrate at the time of the machining and polishing. In the tunnel junction MR head, the thickness of an insulated layer between a magnetization free layer and a magnetization pinned layer is as very small as 20 angstroms or less. In this way, since two ferromagnetic layers are provided adjacent to each other via the thin insulated layer therebetween, the electrical short-circuiting takes place easily between the two ferromagnetic layers in the cutting or polishing step. This problem results from the structural fact that the two ferromagnetic layers arranged as spaced by a very small interval therebetween are both exposed to the air bearing surface.
A second object of the present invention is to provide a tunnel junction MR head which can prevent the electrical short-circuiting between such ferromagnetic layers and can have a high reliability.
In order to attain the first object of the present invention, first and second tunnel junctions are formed at both ends of a magnetization free layer. The word xe2x80x9cthe end of the magnetization free layerxe2x80x9d as used herein means two regions of the magnetization free layer in a track direction separated by its central line and provided at both sides of the central line. The first tunnel junction is defined by one end of the magnetization free layer, a first magnetization pinned layer and a thin insulated layer formed therebetween. The second tunnel junction at the other end of the magnetization free layer is defined by the magnetization free layer, a second magnetization pinned layer and the insulated layer. The first tunnel junction is contacted with the first magnetization pinned layer and connected to a first electrode. The second tunnel junction is contacted with the second magnetization pinned layer and connected to a second electrode. The first and second tunnel junctions are connected each other through the magnetization free layer, so that a detection current flowing from the first electrode is passed to the magnetization free layer through the first tunnel junction and then passed to the second electrode through the second tunnel junction.
In order to attain the second object of the present invention, the sides of the magnetization free layer on its magnetic medium side are projected toward the magnetic medium side from a straight line obtained by connecting the ends of the first and second magnetization pinned layers on the magnetization free layer side. With this structure, the magnetization pinned layers are provided inside the air bearing surface of the magnetic head and are not exposed to the air bearing surface.